Engine air/fuel control systems are known which provide an open loop fuel delivery signal during cold engine operation. Such open loop fuel delivery signal is derived from a measurement of air mass inducted into the engine and a desired air/fuel ratio. After the engine warms, this open loop fuel delivery signal is trimmed by a feedback variable derived from an exhaust gas oxygen sensor to maintain engine operation at stoichiometry. It is also known to correct the open loop fuel delivery signal for delays in fuel delivery to an engine cylinder caused by condensation on the engine intake manifold and intake valve. Until the engine is sufficiently warmed, this condensation will exceed the corresponding evaporation thereby causing a delay in fuel delivery. Compensation to the fuel delivery for this delay is provided by a transient fuel correction value.
The inventor herein has recognized numerous problems with the above approaches. For example, the rate of fuel evaporation will vary with the fuel type. Accordingly, the above described transient fuel correction may not properly correct for transient fuel delay for all fuel types. Further, the open loop fuel delivery signal will not always provide the desired fuel during cold engine operation when different fuel types are used. These occurrences may result in rough cold engine operation.